Semiautomatic, powder-actuated fastener-driving tools are well known, as exemplified by U.S. Pat. Nos. 3,168,744, 3,499,590, 3,552,625, 3,554,425, 3,565,313 and 3,743,159. Powder cartridge feed strips or magazines also are well known in the art, as exemplified by U.S. Pat. No. 3,611,870.
Such tools typically comprise a housing, a barrel mounted in telescoping relation to the housing and adapted to receive at its forward end a fastener which is to be driven by the tool, a chamber for receiving a cartridge, a duct or passageway extending approximately perpendicularly to the main axis of the tool for receiving a cartridge feed strip, strip feeding means for advancing a cartridge feed strip so as to successively position successive cartridges carried by the feed strip in position to enter said chamber, striker means in position to be propelled forward by the hot gases of combustion so as to drive a fastener out of the barrel into a workpiece, and means for firing a cartridge positioned in said chamber so as to cause the striker means to drive a fastener located in the muzzle end of the barrel into a workpiece.
One well known semi-automatic, powder-actuated tool for driving fasteners, hereinafter referred to as the "moving cylinder" tool, consists of a housing having a handle, a cylinder member slidably mounted within the housing having a chamber at its rear end for receiving a cartridge, a barrel member mounted in telescoping relation with the cylinder and housing, the front end or muzzle of said barrel member being adapted to receive a fastener which is to be driven into a workpiece, a fastener-driving striker member slidably disposed in the cylinder and barrel and adapted to be propelled forward by the hot gases produced by the firing of a cartridge in the chamber, a passageway or duct extending along the handle for receiving a cartridge feed strip, strip feeding means for advancing the feed strip one cartridge at a time through the passageway so as to successively locate successive cartridges in position to mate with the firing chamber in the cylinder member, and trigger-operated means for firing a cartridge located in said chamber. After a cartridge has been fired to drive a fastener into a workpiece, the operator causes the cylinder member to be fully extended and then retracted. This action causes the cartridge feedstrip to be advanced so as to move the spent cartridge out of alignment with the chamber and locate the next loaded cartridge in position to mate with the chamber. The rear firing chamber end of the cylinder member has an extension which is in the form of a cylindrical sleeve slotted at three or four circumferentially spaced places so as to provide finger-like sections.
The "moving cylinder" form of powder-actuated tool typically uses a cartridge magazine which consists of a plastic strip with flat oppositely directed face surfaces and holes in which the cartridges are press-fitted. Each side edge of the strip has a plurality of notches for engagement by part of the strip advancing mechanism. The rims of the cartridges protrude from one face surface of the strip. Each cartridge is sized to fit within the cylindrical extension at the rear end of the cylinder member. The finger-like sections of the cylinder member are sized to fit in openings in the feed strip around the chambered cartridge in line with the cartridge rim and serve to partially envelop the casing and engage the rim of the chambered cartridge. When the tool is fired by means of its trigger-operated hammer impacting a cartridge positioned in the chamber, the exploding charge generates gases which drive the striker member forward so as to cause a nail or other fastener positioned in the front end of the barrel member to be driven into a workpiece which is engaged by the barrel member. This form of tool cannot be fired unless the barrel is pressed against a workpiece.
An improved form of "moving cylinder" powder-actuated tool is described in my pending U.S. patent application Ser. No. 497,701, filed May 24, 1983.
As is well known to persons skilled in the art, there are various types of powder cartridges. One of the more common types in the U.S.A. is the 0.22 caliber, star crimped, necked-down cartridge. That particular cartridge and other types of cartridges are available with different loads, i.e., with different powder charges. The charge with the greatest amount of powder is the so-called "red charge" (also known in the industry as the "Power Level 5" cartridge). The next smaller size charge is the so-called "yellow charge". An objective in the industry is to be able to safely use red charge cartridges in a so-called "low velocity tool". Unfortunately cartridges made by various manufacturers frequently exceed the loading tolerences by as much as 20%. Accordingly, in the case of "red charges" used in a low velocity "moving cylinder" tool, if a charge exceeds specifications by 20%, the cartridge may fire in an explosion mode which causes the side wall of the cartridge casing to fracture close to its rim between the finger-like sections of the rear extension of the cylinder member. This mode of explosion is dangerous, may lead to injury to the operator, and also reduces the effectiveness of the charge since some of the combustion gases tend to be lost in a high velocity lateral discharge through the slots in the cylindrical extension on the end of the cylinder member rather than being directed forward so as to drive the fastener which is positioned in the front end of the barrel member. If one cartridge in a magazine is found to have an explosive charge, the whole magazine becomes suspect and may be discarded by the operator to avoid another possibly dangerous situation.
Another problem with the charge magazines of the kind heretofore used in the "moving cylinder" type of power-actuated tools is that a substantial thickness of strip material is disposed between the rim of the cartridge and the extension on the rear end of the cylinder with which the strip is engaged when the tool is fired. Because of this thickness and also because the plastic strip tends to be somewhat compressible, the hammer is required to strike the rim of the cartridge with a substantial force in order to make certain that the cartridge will fire under the impact of the hammer. The required driving force is reduced if the strip is made of a relatively rigid material. However, a somewhat compressible material is required in order to better allow the cartridges to be attached to the strip by a simple press fit. Furthermore, for reasons of economy, it is preferred to make the cartridge strips of relatively low cost materials such as polyethylene which can be injection molded. Unfortunately, such materials tend to deform easily.